OK, I've read some introduction into STK (see the links in the wikipedia article, e.g. this one) and it seems like a relatively simple thing to do.

There is a very limited set of commands flowing between SIM card and ME (phone), so it seems like a relatively simple yet interesting thing to implement. I could try that, but I'm a total newbie regarding maemo - e.g. I'm not sure how to access the SIM card (directly or through dbus or something else?).